Make it possible to build a Completion from a callback (#214)

src/main/java/stormpot/Completion.java

@@ -21,6 +21,7 @@
 import java.util.concurrent.Flow;
 import java.util.concurrent.ForkJoinPool;
 import java.util.concurrent.ForkJoinPool.ManagedBlocker;
+import java.util.function.Consumer;
 
 /**
  * A Completion represents some task that is going to be completed at some
@@ -54,6 +55,20 @@ static Completion from(CompletionStage<?> stage) {
     stage.whenComplete((v, e) -> completion.complete());
     return completion;
   }
+
+  /**
+   * Create a completion using the given callback handler.
+   * The {@link Consumer} argument will be given a {@link Runnable} instance,
+   * which will complete the {@link Completion} when the {@link Runnable#run()} method is called.
+   *
+   * @param completionCallback The handler controlling the completion.
+   * @return A {@link Completion} that completes when the given {@link Runnable#run()} method is called.
+   */
+  static Completion from(Consumer<Runnable> completionCallback) {
+    StackCompletion completion = new StackCompletion();
+    completionCallback.accept(completion::complete);
+    return completion;
+  }
 
   /**
    * Causes the current thread to wait until the completion is finished,

src/main/java/stormpot/internal/StackCompletion.java

@@ -27,7 +27,7 @@
 /**
  * An implementation of {@link Completion} based on a wait-free stack.
  * This implementation also supports a callback mechanism that trigger every time
- * a and {@link #await(Timeout)} or {@link #block()} call is about to block.
+ * an {@link #await(Timeout)} or {@link #block()} call is about to block.
  */
 public final class StackCompletion implements Completion {
   private static final Node END = new Node("END");

src/test/java/stormpot/tests/StackCompletionTest.java

@@ -24,7 +24,6 @@
 
 import java.util.ArrayList;
 import java.util.List;
-import java.util.concurrent.CompletionStage;
 import java.util.concurrent.CyclicBarrier;
 import java.util.concurrent.Flow;
 import java.util.concurrent.Future;
@@ -48,7 +47,6 @@ class StackCompletionTest {
   static final Timeout longTimeout = new Timeout(5, TimeUnit.MINUTES);
 
   protected Completion completion;
-  protected CompletionStage<Object> stage;
 
   @BeforeEach
   void setUp() {

src/test/java/stormpot/tests/StackCompletionWithCallbackTest.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright © 2011-2024 Chris Vest ([email protected])
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package stormpot.tests;
+
+import org.junit.jupiter.api.BeforeEach;
+import stormpot.Completion;
+
+public class StackCompletionWithCallbackTest extends StackCompletionTest {
+  protected Runnable callback;
+
+  @BeforeEach
+  @Override
+  void setUp() {
+    completion = Completion.from(cb -> this.callback = cb);
+  }
+
+  @Override
+  void complete() {
+    callback.run();
+  }
+}

src/test/java/stormpot/tests/StackCompletionWithCompletionStageTest.java

@@ -19,8 +19,11 @@
 import stormpot.Completion;
 
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionStage;
 
 public class StackCompletionWithCompletionStageTest extends StackCompletionTest {
+  protected CompletionStage<Object> stage;
+
   @BeforeEach
   @Override
   void setUp() {